Material property capacitance sensor

ABSTRACT

A system may include a controller configured to cause a capacitance probe to subject a material to a first electric signal having a first frequency and determine a first capacitance of the material at the first frequency. The controller is configured to cause the capacitance probe to subject the material to a second electric signal at a second frequency and determine a second capacitance of the material at the second frequency. The material includes at least a first constituent phase and a second constituent phase. The first constituent phase and the second constituent phase have substantially similar dielectric constants at the first frequency and substantially different dielectric constants at the second frequency. The controller is further configured to determine a porosity of the material based on the first capacitance and determine a relative phase composition of the first constituent phase and the second constituent phase based on the second capacitance.

This application is a continuation of U.S. application Ser. No.15/897,094, filed Feb. 14, 2018, which claims the benefit of U.S.Provisional Application No. 62/458,801, filed Feb. 14, 2017, both ofwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The disclosure relates to material composition and porosity detection.

BACKGROUND

A ceramic matrix composite (CMC) includes ceramic fibers embedded in aceramic matrix. CMCs may have desirable mechanical, physical, andchemical properties such as high fracture toughness, thermal shockresistance, and elongation resistance. CMCs may be used for a variety ofapplications such as gas turbine engines, brake discs, and the like. Anexample CMC is silicon carbide-fiber reinforced silicon carbide(SiC/SiC) composite.

The ceramic fibers and ceramic matrix of a CMC may not be evenlydistributed throughout a CMC article, leading to spatial differences inCMC composition. Further, in some examples, a CMC may include unwantedporosity. For example, a first portion of a CMC article may have adifferent composition of ceramic fibers and matrix material than asecond portion of the CMC article. The CMC article may further include acoating that has an uneven porosity or layer thickness.

SUMMARY

In some examples, the disclosure describes a method that includescausing, by a controller, a capacitance probe to subject a material toan electric signal. The method further includes determining, by thecontroller, a capacitance of the material and a porosity of the materialbased on the capacitance.

In some examples, the disclosure describes a method that includescausing, by a controller, a capacitance probe to subject a material toan electric signal having a frequency. The material includes at least afirst constituent phase and a second constituent phase. The firstconstituent phase and the second constituent phase have substantiallydifferent dielectric constants at the frequency. The method furtherincludes determining, by the controller, a capacitance of the materialat the frequency and a relative phase composition of the firstconstituent phase and the second constituent phase based on thecapacitance.

In some examples, the disclosure describes a method that includescausing, by a controller, a capacitance probe to subject a firstmaterial to a first electric signal. The method further includesdetermining, by the controller, a first capacitance of the firstmaterial. The method further includes causing, by the controller, thecapacitance probe to subject the first material and a second material onthe first material to a second electric signal. The method furtherincludes determining, by the controller, a second capacitance of thefirst material and the second material, and a porosity of the secondmaterial based on the first capacitance and the second capacitance.

In some examples, the disclosure describes a method that includescausing, by a controller, a capacitance probe to subject a firstmaterial to a first electric signal having a frequency. The methodfurther includes determining, by the controller, a first capacitance ofthe first material. The method further includes causing, by thecontroller, the capacitance probe to subject the first material and asecond material on the first material to a second electric signal havingthe frequency. The second material includes at least a first constituentphase and a second constituent phase. The first constituent phase andthe second constituent phase have substantially different dielectricconstants at the frequency. The method further includes determining, bythe controller, a second capacitance of the first material and thesecond material, and a relative phase composition of the firstconstituent phase and the second constituent phase based on the firstcapacitance and the second capacitance.

In some examples, the disclosure describes a system that includes acontroller configured to cause a capacitance probe to subject a materialto an electric signal, determine a capacitance of the material, anddetermine a porosity of the material based on the capacitance.

In some examples, the disclosure describes a system that includes acontroller configured to cause a capacitance probe to subject a materialto an electric signal at a frequency. The material includes at least afirst constituent phase and a second constituent phase. The firstconstituent phase and the second constituent phase have substantiallydifferent dielectric constants at the frequency. The controller isfurther configured to determine a capacitance of the material and arelative phase composition of the first constituent phase and the secondconstituent phase based on the capacitance.

In some examples, the disclosure describes a system that includes acontroller configured to cause a capacitance probe to subject a materialto a first electric signal having a first frequency and determine afirst capacitance of the material at the first frequency. The controlleris configured to cause the capacitance probe to subject the material toa second electric signal at a second frequency and determine a secondcapacitance of the material at the second frequency. The materialincludes at least a first constituent phase and a second constituentphase. The first constituent phase and the second constituent phase havesubstantially similar dielectric constants at the first frequency andsubstantially different dielectric constants at the second frequency.The controller is further configured to determine a porosity of thematerial based on the first capacitance and determine a relative phasecomposition of the first constituent phase and the second constituentphase based on the second capacitance.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages of the disclosure will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual and schematic block diagram illustrating anexample system for determining compositional properties of a materialusing capacitance.

FIG. 2 is a flow diagram illustrating example techniques for determiningporosity or phase composition of a material using capacitance.

FIG. 3A is a diagram of an example system for measuring a capacitance ofa capacitance probe.

FIG. 3B is a diagram of an example system for measuring a capacitance ofa material at a frequency for determining a porosity.

FIG. 3C is a diagram of an example system for measuring a capacitance ofa material at a frequency for determining a phase composition.

FIG. 4 is a flow diagram illustrating an example technique fordetermining open or closed porosity of a material using capacitance.

FIG. 5A is a diagram of an example system for measuring a capacitance ofa capacitance probe.

FIG. 5B is a diagram of an example system for measuring a capacitance ofa material at a frequency for determining a porosity.

FIG. 5C is a diagram of an example system for measuring a capacitance ofa material immersed in electrolyte solution at a frequency fordetermining a porosity.

FIG. 6 is a flow diagram illustrating an example technique fordetermining phase or material composition of a second material on afirst material using capacitance.

FIG. 7A is a diagram of an example system for measuring a capacitance ofa capacitance probe.

FIG. 7B is a diagram of an example system for measuring a capacitance ofa material at a frequency for determining a phase or layer composition.

FIG. 7C is a diagram of an example system for measuring a capacitance ofa first material and a second material at a frequency for determining aphase composition.

FIG. 8 is a flow diagram illustrating an example technique fordetermining open or closed porosity of a second material on a firstmaterial using capacitance.

FIG. 9A is a diagram of an example system for measuring a capacitance ofa capacitance probe.

FIG. 9B is a diagram of an example system for measuring a capacitance ofa material at a frequency for determining a porosity.

FIG. 9C is a diagram of an example system for measuring a capacitance ofa first material and a second material at a frequency for determining aporosity.

FIG. 9D is a diagram of an example system for measuring a capacitance ofa first material and a second material immersed in electrolyte solutionat a frequency for determining a porosity.

FIG. 10 is a schematic diagram of an exemplary bridging circuit used fordetermining a capacitance of a material.

FIG. 11 is a diagram of an example system for determining acompositional property of a material, such as a base material and acoating, using capacitance.

DETAILED DESCRIPTION

The disclosure describes systems and techniques for determiningproperties of a material, including compositions and porosities, usingcapacitance measurements. For example, the systems and techniquesdescribed herein may be used to determine porosity, open porosity,closed porosity, material or phase composition, material thickness, andthe like based on capacitance measurements of the material. In someexamples, the systems and techniques described herein may be performedat a plurality of positions for portions of the material, and acontroller may be configured to generate a representation of one or moreof these characteristics as a function of position. Additionally oralternatively, the systems and techniques described herein may be usedto characterize a base material (e.g., a substrate), and one or morecoating layers by performing the techniques first on the base materialand then on the base material and one or more coating layers.

A capacitance of a material may generally be represented by thefollowing equation:

${C = \frac{ɛ_{0}ɛ_{R}A}{d}},$where ε₀ is an electric field permittivity of free space (also referredto as a “free permittivity”), ε_(R) is a relative permittivity of thematerial, A is the surface area of each of a pair of conductive platesin a capacitance probe, and d is a distance between the pair ofconductive plates. The relative permittivity of the material, ε_(R),(also referred to as a “dielectric constant”, used interchangeablyherein) may represent a permittivity of one or more materials betweenthe pair of conductive plates relative to the permittivity of a vacuum.The relative permittivity of the material may represent the material'sinfluence on an electric field applied to the material. The relativepermittivity, ε_(R), may be generally expressed as a ratio of anabsolute permittivity of the material to the vacuum permittivity;alternatively, the relative permittivity ε_(R) may be expressed as aratio of a capacitance C_(M) of a capacitor using the material as adielectric to a capacitance C₀ of a similar capacitor using a vacuum(or, in the case of a relatively high dielectric of the material, air)as a dielectric. The relative permittivity of the material may generallybe represented by the following equation:

${ɛ_{R} = {\frac{ɛ_{M}}{ɛ_{0}} = \frac{C_{M}}{C_{0}}}},$where ε_(M) is the absolute permittivity of the material, C_(M) is thecapacitance of the material, and C₀ is the vacuum capacitance. The tablebelow shows various static dielectric constants for materials found inCMCs.

Material Dielectric Constant (Static) Air 1 Silicon (Si) 11.7 SiliconCarbine (SiC—3C) 9.72 Silicon Carbine (SiC—6H) 9.66

A material may include more than one constituent. Each constituent maybehave as a dielectric capacitor by contributing to capacitanceaccording to its dimensional and compositional properties, such asthickness, orientation, and relative permittivity. For example, twoconstituents arranged in horizontal layers, such as for a coating, mayhave a total capacitance according to the following equation:

${\frac{1}{C_{M}} = {{\Sigma\frac{1}{C_{N}}} = {\frac{1}{C_{1}} + \frac{1}{C_{2}}}}},$

where C_(N) is the capacitance of each constituent, C₁ is thecapacitance of the first layer, and C₂ is the capacitance of the secondlayer. As another example, two constituents arranged in verticalcolumns, such as at a boundary, may have a total capacitance accordingto the following equation:C _(M) =ΣC _(N) =C ₁ +C ₂,

where C₁ is the capacitance of the first column and C₂ is thecapacitance of the second column. As yet another example, fourconstituents arranged in two vertical columns of two horizontal layerseach may have a total capacitance according to the following equation:

${C_{M} = {\frac{C_{1}C_{2}}{C_{1} + C_{2}} + \frac{C_{3}C_{4}}{C_{3} + C_{4}}}},$

where C₁ is the capacitance of the first layer of the first column, C₂is the capacitance of the second layer of the first column, C₃ is thecapacitance of the first layer of the second column, and C₄ is thecapacitance of the second layer of the second column.

The relative permittivity of a portion of a material may be a functionof various compositional properties of the material, includingchemistry, crystal structure or phase composition, and porosity. In anon-homogenous material, the relative permittivity may depend on variousconstituents of the material between the capacitive plates, such asdifferent crystal structures or phase constitutions, porosity, materialcompositions, and material thicknesses, which may vary throughoutportions of the material. For example, the relative permittivity of asubstantially uniform non-homogeneous material having two or moreconstituents may generally be a summation of the product of a volumefraction and relative permittivity of each constituent, and maygenerally be represented by the following equations:ε_(R)=Σε_(R,i) V _(i) and ΣV _(i)=1,

where i is the constituent, ε_(R,i) is the relative permittivity of theconstituent, and V_(i) is the volume fraction of the constituent.

The relative permittivity of materials may also vary with the frequencyof the electric field applied to the material and temperature of thematerials. For example, two constituent phases in a material may havedifferent dielectric constants at a first frequency and similardielectric constants at a second frequency.

In some examples, a system for determining compositional properties of amaterial may include a capacitance probe and a controller. Thecapacitance probe may be configured to subject the material to at leastone electric signal having a selected frequency. The controller may beconfigured to determine at least one capacitance of the material at thefrequency and determine a compositional property, such as porosity orphase composition, of the material based on the at least onecapacitance.

In some examples, the controller may determine a phase composition ofthe material using capacitance. The material may include at least twoconstituent phases that have substantially different dielectricconstants at at least one frequency. The controller may cause acapacitance probe to subject the material to an electric signal, such asan electric field, having the particular frequency and the controllermay determine the capacitance of the material at the particularfrequency. The controller may determine a relative phase composition ofthe constituent phases based on the relative contribution of eachconstituent phase to the capacitance, e.g., based on the staticdielectric constants of the constituent phases.

In some examples, a controller may determine a porosity of a materialusing capacitance. The material may be homogeneous or may benon-homogeneous with constituent phases having substantially similardielectric constants at a particular frequency. The controller may causea capacitance probe to subject the material to an electric signal, suchas an electric field, at the particular frequency, and the controllermay determine a capacitance of the material. The controller maydetermine a porosity of the material based on the relative contributionof the material and the pore medium to the capacitance, e.g., based onthe static dielectric constants of the constituent phases.

In some examples, the controller may determine a phase compositionand/or a porosity of a material using capacitance at differentfrequencies to allow for differentiation of more than two constituents.The material may have a first constituent phase, a second constituentphase, and pores with a pore medium. The first constituent phase and thesecond constituent phase may have different dielectric constants at afirst frequency and similar dielectric constants at a second frequency,while the pore medium may have a substantially constant dielectricconstant that is significantly smaller than the dielectric constants ofthe first constituent phase and the second constituent phase. Todetermine relative phase composition, the controller may cause thecapacitance probe to subject the material to an electric signal at thefirst frequency. The controller may determine a relative phasecomposition of the constituent phases based on the relative contributionof each constituent phase to the capacitance, as the first constituentphase and the second constituent phase may have substantially differentdielectric constants at the first frequency and their respective phasecompositions may be differentiated. To determine porosity, thecontroller may cause the capacitance probe to subject the material to anelectric signal at the second frequency. The controller may determine aporosity based on the relative contribution of the pore medium and thefirst and second constituent phases to the capacitance, as the firstconstituent phase and the second constituent phase may havesubstantially similar dielectric constants at the second frequency andthe porosity may be differentiated.

In some examples, the controller may determine a volume fraction of openporosity and a volume fraction of closed porosity, or volumetric ratioof both, using capacitance measurements. The material may include bothopen and closed pores. The controller may cause a capacitance probe tosubject the material to an electric signal and controller may determinethe capacitance of the material. In a separate measurement, the materialmay be submerged in an electrolyte solution, which may substantiallyfill open pores of the material and remove the contribution of air inthe open pores to the capacitance. The capacitance probe may subject thematerial to the electric signal and the controller may determine acapacitance of the material while the material is submerged in theelectrolyte solution. The controller may determine a volume fraction ofclosed porosity and a volume fraction of open porosity of the materialbased on the relative difference in the capacitance of the material withand without the electrolyte solution.

In some examples, a controller may use capacitance measurements toevaluate characteristics of a second material, such as a coating, on afirst material, such as a substrate. For example, after determining acapacitance of the first material as described above, the secondmaterial may be deposited or applied to the first material. Thecontroller then may cause the capacitance probe to subject thecombination of the first material and the second material to an electricsignal and may determine a capacitance of the first material and thesecond material. The controller may determine the porosity of the secondmaterial based on the difference between the first capacitance and thesecond capacitance, and the relative contribution of the second materialand the pore medium to the difference in capacitance. In some examples,if the porosity of the second material is outside of a predeterminedrange, the first and second material may be rejected or undergo furtherprocessing.

These techniques may provide faster and less expensive non-destructivemethods for determining compositional properties of materials, e.g.,compared to mercury porosimetry, electron microscopy, x-ray tomography,gravimetric methods, or the like.

FIG. 1 is a conceptual and schematic block diagram illustrating anexample system 2 for determining compositional properties of a material8 using capacitance. System 2 includes capacitance probe 4 andcontroller 16. In some examples, as shown in FIG. 1, system 2 mayoptionally include vessel 6, electrolyte source 10, gantry system 14,user interface device 19, or any combination thereof.

Material 8 may include any material having a dielectric constant capableof affecting an electric field applied to material 8 by capacitanceprobe 4. In some examples, material 8 may be a material having at leasttwo phase constituents. For example, material 8 may have a firstconstituent phase having a first crystal structure and a secondconstituent phase having a second crystal structure. Each constituentphase may have an associated dielectric constant. In some examples, atleast two constituent phases have substantially similar dielectricconstants. In some examples, at least two constituent phases havesubstantially different dielectric constants. The dielectric constantsmay change as a function of applied frequency, and, in some examples,the first dielectric constant may change differently with appliedfrequency than the second dielectric constant. In some instances, thefirst and second dielectric constants may be substantially the same at afirst frequency and different at a second frequency.

In some examples, material 8 may be a porous material. A porous materialmay include any material with open pores, closed pores, or bothcontaining a pore medium different than the porous material. Forexample, the pore medium may include air. Porous materials may include,but are not limited to, polymers, foams, composites, and the like.

In some examples, material 8 may have more than one constituent, such asmore than one layer. For example, material 8 may include a firstmaterial, such as substrate, and a second material on the first materialas a coating. Example substrates include metals, alloys, ceramics,ceramic matrix composites, and the like. Example coatings include bondcoatings, thermal barrier coatings (TBCs), environmental barriercoatings (EBCs), calcia-magnesia-alumina-silicate (CMAS) resistantcoatings, abradable coatings, and the like.

In some examples, material 8 may include a ceramic matrix composite(CMC). A CMC may include ceramic reinforcement material and ceramicmatrix material. In some examples, material 8 may include a plurality ofCMC layers. For example, a first CMC layer may be selected to carry anapplied load, while a second CMC layer may be selected to transfer theapplied load to an underlying component. In some examples, thecomposition of the ceramic matrix material is the same as thecomposition of the ceramic reinforcement material. The ceramic matrixmaterial may include, but is not limited to, silicon carbide (SiC),silicon nitride (Si₃N₄), alumina (Al₂O₃), aluminosilicate (e.g.,Al₂SiO₅), silica (SiO₂), molybdenum carbide (Mo₂C), and the like.

The composition, shape, size, and the like, of the ceramic reinforcementmaterial may be selected to provide the desired properties to the CMC.In some examples, the ceramic reinforcement material may be chosen toincrease the toughness of a brittle matrix material. In some examples,the ceramic reinforcement material may provide structural support tomaterial 8. The ceramic matrix material may be chosen to modify athermal conductivity, electrical conductivity, thermal expansioncoefficient, hardness, or the like, of material 8. The ceramicreinforcement material may include, but is not limited to, SiC, Si₃N₄,Al₂O₃, aluminosilicate, SiO₂, Mo₂C, and the like. The ceramic fibers mayhave a variety of configurations including, but not limited to,discontinuous forms such as whiskers, platelets, or particulates, orcontinuous forms, such as a continuous monofilament or multifilamentweave. In some examples, the ceramic reinforcement material may be thesame composition as the ceramic matrix material.

In some examples, material 8 may include a coating. The coating may beselected to provide protective or functional properties to material 8.The coating may include, for example, an EBC, a TBC, a CMAS-resistantcoating, an abradable coating, or the like. In some examples, a singlecoating may perform two or more of these functions. For example, an EBCmay provide environmental protection, thermal protection, andCMAS-resistance to material 8. In some examples, instead of including asingle coating, material 8 may include a plurality of overlyingcoatings, such as at least one EBC, at least one TBC layer, at least oneCMAS-resistant layer, at least one abradable coating, or combinationsthereof.

In some examples, material 8 may include a bond coat that includes anyuseful material to improve adhesion between a first layer of material 8(e.g., a substrate) and subsequent layer(s) applied to the bond coat.For example, the bond coat may be formulated to exhibit desired chemicalor physical attraction between a CMC and any subsequent coating appliedto the bond coat. In some examples, the bond coat may include siliconmetal, alone, or mixed with at least one other constituent including,for example, at least one of a transition metal carbide, a transitionmetal boride, or a transition metal nitride. Representative transitionmetals include, for example, Cr, Mo, Nb, W, Ti, Ta, Hf, or Zr. In someexamples, the bond coat may additionally or alternatively includemullite (aluminum silicate, Al₆Si₂O₁₃), silica, silicon carbide, asilicide, a rare earth silicate, or the like, alone, or in anycombination (including in combination with one or more of silicon metal,a transition metal carbide, a transition metal boride, or a transitionmetal nitride).

Additionally or alternatively, a coating of material 8 may include anEBC, which may provide environmental protection, thermal protection,and/or CMAS-resistance to material 8. An EBC may include materials thatare resistant to oxidation or water vapor attack, and/or provide atleast one of water vapor stability, chemical stability and environmentaldurability to material 8. In some examples, the EBC may be used toprotect a CMC against oxidation and/or corrosive attacks at highoperating temperatures. An EBC coating may include at least one of afree rare earth oxide, silica, alumina, a rare earth silicate, analuminosilicate, or an alkaline earth aluminosilicate. For example, anEBC coating may include mullite, barium strontium aluminosilicate(BSAS), barium aluminosilicate (BAS), strontium aluminosilicate (SAS),at least one free rare earth oxide, at least one rare earth monosilicate(RE₂SiO₅, where RE is a rare earth element), at least one rare earthdisilicate (RE₂Si₂O₇, where RE is a rare earth element), or combinationsthereof. The rare earth element in the at least one free rare earthoxide, the at least one rare earth monosilicate, or the at least onerare earth disilicate may include at least one of Lu (lutetium), Yb(ytterbium), Tm (thulium), Er (erbium), Ho (holmium), Dy (dysprosium),Tb (terbium), Gd (gadolinium), Eu (europium), Sm (samarium), Pm(promethium), Nd (neodymium), Pr (praseodymium), Ce (cerium), La(lanthanum), Y (yttrium), or Sc (scandium). In some examples, the atleast one rare earth oxide includes an oxide of at least one of Yb, Y,Gd, or Er.

In some examples, the EBC coating may have a dense microstructure, acolumnar microstructure, or a combination of dense and columnarmicrostructures. A dense microstructure may be more effective inpreventing the infiltration of CMAS and other environmentalcontaminants, while a columnar microstructure may be more straintolerant during thermal cycling. A combination of dense and columnarmicrostructures may be more effective in preventing the infiltration ofCMAS or other environmental contaminants than a fully columnarmicrostructure while being more strain tolerant during thermal cyclingthan a fully dense microstructure. In some examples, an EBC coating witha dense microstructure may have a porosity of less than about 20 vol. %,such as less than about 15 vol. %, less than 10 vol. %, or less thanabout 5 vol. %, where porosity is measured as a percentage of porevolume divided by total volume of the EBC coating.

In some examples, the EBC may act as a thermal barrier coating (TBC).The TBC may include at least one of a variety of materials having arelatively low thermal conductivity, and may be formed as a porous or acolumnar structure in order to further reduce thermal conductivity ofthe TBC and provide thermal insulation to material 8. In some examples,the TBC may include materials such as ceramic, metal, glass, or thelike. In some examples, the TBC may include silicon carbide, siliconnitride, boron carbide, aluminum oxide, cordierite, molybdenumdisilicide, titanium carbide, stabilized zirconia, stabilized hafnia, orthe like.

Additionally or alternatively, a coating may include an abradable layer.The abradable layer may include at least one of a free rare earth oxide,a rare earth silicate, an aluminosilicate, or an alkaline earthaluminosilicate. For example, an EBC coating may include mullite, bariumstrontium aluminosilicate (BSAS), barium aluminosilicate (BAS),strontium aluminosilicate (SAS), at least one free rare earth oxide, atleast one rare earth monosilicate (RE₂SiO₅, where RE is a rare earthelement), at least one rare earth disilicate (RE₂Si₂O₇, where RE is arare earth element), or combinations thereof.

The abradable layer may be porous. Porosity of the abradable layer mayreduce a thermal conductivity of the abradable layer and/or may affectthe abradability of the abradable layer. In some examples, the abradablelayer includes porosity between about 10 vol. % and about 50 vol. %. Inother examples, the abradable layer includes porosity between about 15vol. % and about 35 vol. %, or about 20 vol. %. Porosity of theabradable layer is defined herein as a volume of pores or cracks in theabradable layer divided by a total volume of the abradable layer(including both the volume of material in the abradable layer and thevolume of pores/cracks in the abradable layer).

System 2 may include vessel 6. Vessel 6 may be configured to housematerial 8 and part or all of capacitance probe 4, such as capacitanceelectrodes 18. Vessel 6 may also include equipment related toelectrolyte source 10 or gantry system 14. For example, vessel 6 mayinclude equipment for distributing electrolyte solution to at least onesurface of material 8, such as a spray device. As another example,vessel 6 may include insulators, baffles, or gaskets for containingelectrolyte solution. As another example, vessel 6 may include part orall of gantry system 14, such as linear drive actuators coupled tocapacitance electrodes 18.

System 2 may include electrolyte source 10. Electrolyte source 10 may beconfigured to provide vessel 6 with electrolyte solution for applicationof electrolyte solution to material 8. In some examples, electrolytesource 10 may be communicatively coupled to controller 16. In someexamples, controller 16 may control flow of electrolyte solution tomaterial 8, such as by changing a position of a flow rate valve. Theelectrolyte of electrolyte source 10 may include any electrolyte thatexhibits a substantially small effect on capacitance. In some examples,the electrolyte of electrolyte source 10 may have a dielectric constantof less than 0.1.

System 2 may include gantry system 14. Gantry system 14 may beconfigured to change the spatial relationship between capacitance probe4 and material 8 for determination of a capacitance of at least twoportions of material 8. Gantry system 14 may move material 8,capacitance electrodes 18, or any combination thereof. For example,gantry system 14 may move capacitance electrodes 18 along an x-y planeof material 8. Gantry system 14 may include, but is not limited to,linear drive systems, articulation systems, or other gantry positioningsystem. In some example, gantry system 14 may be communicatively coupledto controller 16. In some examples, controller 16 may control thepositioning of gantry system 14, which may include capacitive electrodes18, such as by controlling a linear drive of an actuator.

System 2 includes capacitance probe 4. Capacitance probe 4 may includecapacitance electrodes 18A and 18B (referred to collectively as“capacitance electrodes 18”) and oscillator 12. Capacitance probe 4 maybe configured to subject material 8 to an electric signal and returnfeedback to controller 16. The electric signal may be an oscillatingelectric field having a selected frequency. Capacitance probe 4 mayoutput, such as to controller 16, an indication signal, such as avoltage, that corresponds to the capacitance of material 8, or acombination of materials between capacitance electrodes 18. Thecapacitance may be a function of a dielectric constant of material 8, aswell as dielectric constants of other materials affecting capacitanceprobe 4.

Capacitance probe 4 may include at least a pair of capacitanceelectrodes 18 configured to function as capacitor plates, each platehaving an area. Capacitance electrodes 18 may be separated by a distancethat defines a gap. Capacitance electrodes 18 may be spaced toaccommodate material 8, so that material 8 may be placed in the gapbetween capacitance electrodes 18. Materials in the gap betweencapacitance electrodes 18 having a dielectric constant may affect thecapacitance between capacitance electrodes 18.

Capacitance probe 4 also may include oscillator 12. Oscillator 12 may beelectrically coupled to capacitance electrodes 18. Oscillator 12 may beconfigured to produce an alternating electric field between capacitanceelectrodes 18. The alternating electric field may have a selectedfrequency. Further, oscillator 12 may be configured to detect feedbackfrom at least one of capacitance electrodes 18 that corresponds to acapacitance between capacitance electrodes 18. Oscillator 12 mayinclude, for example, a capacitor, an inductor, a power source, or thelike.

System 2 also includes controller 16, which is communicatively coupledto at least capacitance probe 4. Controller 16 may also becommunicatively coupled to electrolyte source 10, gantry system 14, orboth. Controller 16 may include any of a wide range of devices,including processors (e.g., one or more microprocessors, one or moreapplication specific integrated circuits (ASICs), one or more fieldprogrammable gate arrays (FPGAs), or the like), one or more servers, oneor more desktop computers, one or more notebook (i.e., laptop)computers, one or more cloud computing clusters, or the like.

Controller 16 may be configured to receive or include propertyinformation related to material 8. Property information may include anyinformation that may be used to determine compositional properties ofmaterial 8. Property information may include, but is not limited to:dielectric constants, such as for constituent phases of material 8,compositions or constituents of material 8, and pore media of material8; thicknesses, such as for portions of material 8 (e.g., a substrate, acoating layer, or the like); dielectric constants as a function offrequency, such as for constituent phases of material 8, compositions ofmaterial 8, and pore media of material 8; and the like. In someexamples, controller 16 may determine and store property informationrelated to dielectric constants and their variance with frequency. Forexample, controller 16 may include storage that stores propertyinformation in a database.

Controller 16 may be configured to generate a representation of material8 as a function of portion of material 8. Controller 16 may beconfigured to cause user interface device 19 to output therepresentation. For example, the representation may be a spatial mapthat includes spatial compositional property information of thematerial, such as capacitance, permittivity, porosity, phasecomposition, layer composition, open/closed porosity, and the like. Thespatial information may be stored, for example, in a database incontroller 16 and any changes in the materials may be tracked.

Controller 16 may be configured to cause capacitance probe 4 to subjectmaterial 8 to one or more electric signals having selected frequencies.For example, controller 16 may send a control signal to capacitanceprobe 4 to cause capacitance probe 4 to generate a desired voltage witha desired frequency. In some examples, controller 16 may include voltageand frequency information in the control signal.

Controller 16 may be configured to determine the capacitance of material8. Controller 16 may receive feedback from capacitance probe 4 anddetermine a capacitance from the feedback. For example, capacitanceprobe 4 may detect a particular voltage change over a period of time anddetermine a capacitance from the voltage change and the period of time.An example circuit with which controller 16 may determine capacitance isshown in FIG. 10. FIG. 10 is a schematic diagram of an exemplarybridging circuit for determining a capacitance. Two known resistors, R,and a variable standard capacitance, C_(s), may be used to determine anunknown capacitance, C_(X), of material 8.

Controller 16 may be configured to determine a compositional property ofmaterial 8 based on capacitance. In some examples, controller 16 may beconfigured to determine a porosity of a material using a capacitancemeasurement. For example, controller 16 may receive dielectriccoefficient information for material 8 (or constituents of material 8)and a pore medium, such as air, at a particular frequency. Controller 16may determine a relative contribution of the material and pore medium tomeasured capacitance based on the measured capacitance, the dielectricinformation associated material 8 and the pore medium, the thickness ofmaterial 8, and the like. Controller 16 may correlate the relativecontribution of the material and pore medium to porosity for theparticular portion of material 8 being analyzed.

In some examples, controller 16 may be configured to determine a phasecomposition of a material having at least a first constituent and asecond constituent of material 8. For example, controller 16 may receivedielectric information for two or more constituent phases of material 8at one or more frequencies. Based on the capacitance and the dielectricinformation for the two or more constituent phases, controller 16 maydetermine a relative contribution of each of the two or more constituentphases to capacitance. Other constituents may include, but are notlimited to, crystal structures, components, and other structures thatmay exhibit differences in dielectric constants throughout material 8.In some examples, the first and second constituents may be differentcompositions. For example, in a silicon carbide (SiC)/silicon (Si)material, the first constituent may include SiC and the secondconstituent may include Si. In some examples, the first and secondconstituents may be different phases of the same composition. Forexample, in a SiC/SiC CMC material, the first constituent phase mayinclude α-SiC and the second constituent phase may include β-SiC.

In some examples, controller 16 may be configured to determine a closedand open porosity of a material. For example, controller 16 maydetermine a closed and open porosity of the material based on dielectricinformation of the material at a particular frequency, as well as afirst capacitance of the material and pore medium and a secondcapacitance of the material and an electrolyte. Based on a differencebetween the first capacitance and the second capacitance, controller 16may determine a relative contribution of open pores, corresponding tothe first capacitance, and closed pores, corresponding to the secondcapacitance, of the material. Controller 16 may cause electrolyte source10 to provide electrolyte solution to vessel 6. The electrolyte solutionmay permeate into open pores of one or more surfaces of material 8. Forexample, controller 16 may cause vessel 6 to fill with electrolytesolution, or controller 16 may selectively spray or immerse a surfacewith electrolyte solution. Controller 16 may allow for the electrolytesolution to substantially permeate and the second capacitance to reachsteady state before determining the second capacitance measurement. Forexample, permeation may vary with time based on properties of theelectrolyte solution and the open pores of material 8, such as viscosityof the electrolyte solution, size of the open pores, surface tension,lubricity, temperature, and the like. In examples having a highlyviscous electrolyte solution, substantially all open pores may be filledwhen, for example, greater than 90% of open pore volumes has beenfilled. In some examples, substantially all open pores may be filledwhen a steady state capacitance has been reached.

In some examples, controller 16 may be configured to determine a coatingcomposition of a coating having two or more layer materials. Forexample, controller 16 may determine a coating composition of thecoating based on dielectric information of one or more layers of thecoating, as well as a first capacitance of the underlying material and asecond capacitance of the coating at one or more frequencies. Controller16 may determine a difference between the first capacitance and thesecond capacitance and determine a relative contribution of each of thecoatings based on that difference.

In some examples, controller 16 may be configured to determine aporosity of a coating. For example, controller 16 may determine aporosity of a coating based on dielectric information of an underlyingmaterial, the coating, and the coating pore medium at a particularfrequency, as well as a first capacitance of the underlying material anda second capacitance of the coating. Controller 16 may determine adifference between the first capacitance and the second capacitance anddetermine a relative contribution of the coating and the coating poremedium based on that difference.

Controller 16 may be configured to perform any of the techniques abovefor one or more portions of material 8. Controller 16 may be configuredto control gantry system 14 to reposition capacitance electrodes 18 ofcapacitance probe 4 to different portions of material 8. For example,controller 16 may cause capacitance probe 4 to subject material 8 to afirst electric signal, determine a first capacitance of material 8, anddetermine a porosity of material 8 based on the first capacitance.Controller 16 may cause capacitance probe 4 to be positioned over adifferent portion of material 8, such as by controller gantry system 14.Controller 16 may then cause capacitance probe 4 to subject thedifferent portion of material 8 to a second electric signal, determine asecond capacitance of the different portion of material 8, and determinea porosity of the second portion of material 8 based on the secondcapacitance. Controller 16 may generate a representation of porosity ofmaterial 8 as a function of portion of material 8 and cause userinterface device 19 to output the representation of porosity.

Further operation of controller 16 in system 2 will be described withreference to a controller communicatively coupled to a capacitance probeof FIGS. 2-9.

In some examples, system 2 of FIG. 1 may determine a porosity or phasecomposition of material 8. For example, a material, such as material 8,may be used for a high stress part that requires a porosity of material8 that is below a particular threshold. In another example, the samepart may require a substantially homogenous distribution of crystalstructures. FIG. 2 is a flow diagram illustrating example techniques fordetermining porosity (21), determining phase composition (23), ordetermining both, of material 8. The techniques of FIG. 2 will bedescribed with concurrent reference to FIGS. 3A-3C, although one ofordinary skill will understand that the techniques of FIG. 2 may beperformed by other systems that include more or fewer components, andthat system 40 of FIGS. 3A-3C may perform other techniques. FIGS. 3A-3Care diagrams of an example system 40 for determining a porosity or phasecomposition of a material 52. Components of FIGS. 3A-3C may besubstantially the same as similar components of FIG. 1. For example,system 2, capacitance probe 4, material 8, oscillator 12, capacitanceelectrodes 18A and 18B, and controller 16 may correspond to system 40,capacitance probe 42, material 52, oscillator 46, capacitance electrodes44 and 48, and a controller (not shown), respectively.

FIG. 3A is a diagram of an example system for measuring a capacitance ofa capacitance probe 42. Capacitance probe 42 includes oscillator 46 andcapacitance electrodes 44, 48. Before positioning a material 52 in airgap 50, a controller (not shown), such as controller 16 of FIG. 1, mayfirst determine a free permittivity of capacitance probe 42 and air gap50 by using the capacitance of capacitance probe 42 and air gap 50. Thefree permittivity ε₀ represents the electric field permittivity causedby capacitance probe 42 and air gap 50 (e.g., air may have a dielectricconstant of 1). The controller may cause capacitance probe 42 to subjectair gap 50 to an electric signal. The controller may detect anddetermine a capacitance of the air gap 50. The capacitance may berepresented by the following equation:

${C_{0} = \frac{ɛ_{0}A}{d_{0}}},$

Where C₀ is the capacitance of capacitance probe 42 and air gap 50, ε₀is the free permittivity, A is the area of each of capacitanceelectrodes 44, 48, and do is a distance between capacitance electrodes44, 48 filled by air gap 50. The controller may determine the freepermittivity ε₀ for capacitance probe 42 and air gap 50 based on themeasured capacitance C₀ and the known values for A and do.

Referring back to FIG. 2, system 40 may use the techniques of FIG. 2 todetermine a porosity of a portion of material 52 (21). The technique ofFIG. 2 may include causing, by a controller, capacitance probe 42 tosubject material 52 to an electric signal having a frequency f_(Po)(20). In examples in which material 52 includes multiple constituentphases or compositions and system 40 is determining porosity of material52, the frequency may be selected so that the constituent phases orcompositions have substantially similar dielectric constants at theparticular frequency. For example, at a frequency of about 2 GHz, alphaSiC and beta SiC may both have a dielectric constant of about 20. FIG.3B is a diagram of system 40 for measuring a capacitance of material 52at frequency f_(Po) for determining a porosity of a portion of material52. The portion of material 52 may be the portion between capacitanceelectrodes 44, 48. Material 52 may have a thickness d_(M), while air gap50 may have a new thickness d_(A) due to space taken up by material 52.Material 52 may include a single constituent phase, or material 52 mayinclude two or more constituent phases.

The technique of FIG. 2 may further include determining, by thecontroller, a capacitance of material 52 at the frequency f_(Po) (22).The controller may measure an equivalent capacitance C_(eq,Po) betweencapacitance electrodes 44, 48, including a capacitance C_(Po) ofmaterial 52 at frequency f_(Po) and a capacitance C_(A) of air gap 50 atfrequency f_(Po). The equivalent capacitance C_(eq,Po) of material 52and air gap 50 may be represented by the following equation:

$C_{{eq},{Po}} = \left( {\frac{1}{C_{A}} + \frac{1}{C_{Po}}} \right)^{- 1}$

The capacitance C_(A) of air gap 50 may be represented by the followingequation:

${C_{A} = \frac{ɛ_{0}A}{d_{0} - d_{M}}},$

while the capacitance C_(Po) of material 52 at frequency f_(Po) may berepresented by the following equation:

${C_{Po} = \frac{ɛ_{Po}ɛ_{0}A}{d_{M}}},$

where ε_(Po) is the relative permittivity of material 52 at frequencyf_(Po) and d_(M) is the thickness of material 8. In some examples, thecontroller may use the C_(A) determined in the first measurement, freepermittivity ε₀, and equivalent capacitance C_(eq,Po) to determine thecapacitance C_(Po) of material 52 at frequency f_(Po) to determineε_(Po).

The technique of FIG. 2 may further include determining, by thecontroller, a porosity of material 52 (24). The controller may use anytechnique that determines a volume fraction of pore medium fromcapacitance C_(Po) of material 52 at frequency f_(Po). In some examples,the controller may determine a volume fraction of material 52 and poremedium by evaluating the relative permittivity ε_(Po) of material 52 atfrequency f_(Po) with respect to the dielectric constant of material 52and the dielectric constant of air. For example, the volume fraction ofmaterial 8 and air may be represented by the following equations:ε_(R)=ε_(M) V _(M)+ε_(A) V _(A) and V _(M) +V _(A)=1,

where ε_(M) is the relative permittivity of non-porous material 8, V_(M)is the volume fraction of nonporous material 8, C_(A) is the relativepermittivity of air, and V_(A) is the volume fraction of air. If therelative permittivity ε_(Po) of SiC material 52 at frequency f_(Po) is19.5, the relative permittivity C_(A) of air is 1, and the relativepermittivity ε_(M) of nonporous SiC is 20, then the porosity of material52 may be about 7%.

Additionally or alternatively, system 40 may use the techniques of FIG.2 to determine a phase composition of material 52 (23) having at least afirst constituent phase and a second constituent phase. The technique ofFIG. 2 may include causing, by the controller, capacitance probe 42 tosubject material 52 to an electric signal having a frequency f_(Ph)(26). The frequency f_(Ph) may be selected so that the first constituentphase and the second constituent phase of material 52 have substantiallydifferent dielectric constants at the frequency f_(Ph). For example, ata frequency of 1 GHz, alpha SiC may have a dielectric constant of about20, while beta SiC may have a dielectric constant of about 35. FIG. 3Cis a diagram of system 40 for measuring a capacitance of material 52 ata frequency f_(Ph) for determining a phase composition of material 52.

The technique of FIG. 2 may further include determining, by thecontroller, a capacitance of material 52 at frequency f_(Ph) (28). Thecontroller may measure an equivalent capacitance C_(eq,Ph) betweencapacitance electrodes 44, 48, including a capacitance C_(Ph) ofmaterial 52 at frequency f_(Ph) and a capacitance C_(A) of air gap 50 atfrequency f_(Po). The equivalent capacitance C_(eq,Ph) may berepresented by the following equation:

$C_{{eq},{Ph}} = \left( {\frac{1}{C_{A}} + \frac{1}{C_{Ph}}} \right)^{- 1}$

The capacitance C_(Ph) of material 52 at frequency f_(Ph) may berepresented by the following equation:

${C_{Ph} = \frac{ɛ_{Ph}ɛ_{0}A}{d_{M}}},$

where ε_(Ph) is the relative permittivity of material 52 at frequencyf_(Ph). In some examples, the controller may use the C_(A) determined inthe first measurement, free permittivity ε₀, and the equivalentcapacitance C_(eq,Ph), to determine the capacitance C_(Ph) of material52 at frequency f_(Ph) to determine the relative permittivity ε_(Ph) ofmaterial 52 at frequency f_(Ph).

The technique of FIG. 2 may further include determining, by thecontroller, a relative phase composition of material 52 (30). In someexamples, the controller may determine a contribution of each of thefirst constituent phase dielectric constant and the second constituentphase dielectric constant to the relative permittivity ε_(Ph) ofmaterial 52 at frequency f_(Ph). For example, the volume fraction of thefirst and second constituent phases of material 52 may be represented bythe following equations:ε_(R)=ε_(M,1) V _(M,1)+ε_(M,2) V _(M,2) and V _(M,1) +V _(M,2)=1,

where ε_(M,1) is the relative permittivity of the first constituentphase, V_(M,1) is the volume fraction of the first constituent phase,ε_(M,2) is the relative permittivity of the second constituent phase,and V_(M,2) is the volume fraction of the second constituent phase. Forexample, if the relative permittivity ε_(Ph) of SiC material 52 atfrequency f_(Ph) is 25, the dielectric constant of alpha SiC is 20, andthe dielectric constant of beta SiC is 35, then the relative phasecomposition at the particular portion of material 52 based on volumefraction may be ⅔ alpha SiC and ⅓ beta SiC. Alternatively, a volumetricratio of the volume fractions of the first constituent phase and thesecond constituent phase may be used.

The technique of FIG. 2 may further include causing, by the controller,capacitance probe 42 to be positioned over a different portion ofmaterial 52. Before steps 20 or 26 discussed above, the controller maycause capacitance probe 42 to be positioned over a portion of material52 (32). After determining a porosity or relative phase composition ofmaterial 52, as in steps 24 and 30, the controller may determineadditional portions of material 52 for which to determine a porosity orrelative phase composition (34). The controller may cause capacitanceprobe 42 to be positioned over a different portion of material 52 (32).The controller may generate a representation of a porosity, a relativephase composition, or both, as a function of portion of material 52(36). The controller may cause a user interface device to output therepresentation of the porosity, the relative phase composition, or both(38).

By using the techniques of FIG. 2, a system 2 may relatively quickly andrelatively inexpensively determine a porosity or phase composition of amaterial. For example, an x-ray or other radiographic scan of thematerial may be costly and require a significant amount of time tocomplete. In contrast, the techniques of FIG. 2 may allow for real-timescanning of an article that includes the material to generate, forexample, a composition map of porosity, phase composition, or otherproperty for the article. The techniques of FIG. 2 may be feasible for awide range of articles whose alternative costs of performanceevaluation, such as quality control, may be prohibitive.

In addition to determining porosity of material 52, the techniquesdiscussed herein may be used to determine an open and closed porosity ofmaterial 52. For example, a material used in fluid environments maypreferably have a low permeability that corresponds to a low fraction ofopen pores to closed pores, or a barrier coating may include a lowfraction of open porosity to reduce a permeability of the coating tofluids. FIG. 4 is a flow diagram illustrating an example technique fordetermining open and closed porosity of a material using capacitance(61). The technique of FIG. 4 will be described with concurrentreference to FIGS. 5A-5C and previously described FIG. 2, although oneof ordinary skill will understand that the technique of FIG. 4 may beperformed by other systems that include more or fewer components, andthat system 2 may perform other techniques. FIGS. 5A-5C are diagrams ofan example system 80 for determining an open and closed porosity ofmaterial 52 using capacitance. Components of FIGS. 5A-5C may besubstantially the same as similar components of FIG. 1. For example,system 2, capacitance probe 4, material 8, oscillator 12, capacitanceelectrodes 18A and 18B, and controller 16 may correspond to system 40,capacitance probe 42, material 52, oscillator 46, capacitance electrodes44 and 48, and a controller (not shown), respectively.

FIG. 5A is a diagram of system 80 for measuring a capacitance of acapacitance probe 42, which may be operably similar to FIG. 3A describedabove. Capacitance probe 42 includes oscillator 46 and capacitanceelectrodes 44, 48. Before positioning a material 52 in air gap 50, acontroller (not shown), such as controller 16 of FIG. 1, may firstdetermine a free permittivity of capacitance probe 42 and air gap 50 byusing the capacitance of capacitance probe 42 and air gap 50. The freepermittivity ε₀ represents the electric field permittivity caused bycapacitance probe 42 and air gap 50 (e.g., air may have a dielectricconstant of 1). The controller may cause capacitance probe 42 to subjectair gap 50 to an electric signal. The controller may detect anddetermine a capacitance of the air gap 50. The capacitance may berepresented by the following equation:

${C_{0} = \frac{ɛ_{0}A}{d_{0}}},$

Where C₀ is the capacitance of capacitance probe 42 and air gap 50, ε₀is the free permittivity, A is the area of each of capacitanceelectrodes 44, 48, and d₀ is a distance between capacitance electrodes44, 48 filled by air gap 50. The controller may determine the freepermittivity ε₀ for capacitance probe 42 and air gap 50 based on themeasured capacitance C₀ and the known values for A and d₀.

Referring back to FIG. 4, system 80 may use the techniques of FIG. 4 todetermine an open and closed porosity of a portion of material 52 usingcapacitance (61). The technique of FIG. 4 may include causing, by thecontroller, capacitance probe 42 to subject material 52 to an electricsignal having a frequency f_(Po) (60). In examples in which material 52includes multiple constituent phases or compositions, the frequency maybe selected so that the constituent phases or compositions havesubstantially similar dielectric constants at the particular frequency.

FIG. 5B is a diagram of system 80 for measuring a capacitance ofmaterial 52 at a frequency for determining a porosity of material 52.The portion of the material 52 may be the portion between capacitanceelectrodes 44, 48. Material 52 may have a thickness d_(M), while air gap50 may have a new thickness d_(A) due to space taken up by material 52.Material 52 may include a single constituent phase, or material 52 mayinclude two or more constituent phases.

The technique of FIG. 4 may further include determining, by thecontroller, a capacitance C_(Po) of material 52 at frequency f_(Po),such as described in step 22 of FIG. 2 (62). The controller may measurean equivalent capacitance C_(eq,Po) between capacitance electrodes 44,48, including a capacitance C_(Po) of material 52 at frequency f_(Po)and a capacitance C_(A) of air gap 50. The equivalent capacitanceC_(eq,Po) may be represented by the following equation:

$C_{{eq},{Po}} = \left( {\frac{1}{C_{A}} + \frac{1}{C_{Po}}} \right)^{- 1}$

The capacitance C_(A) of air gap 50 may be represented by the followingequation:

${C_{A} = \frac{ɛ_{0}A}{d_{0} - d_{M}}},$

while the capacitance C_(Po) of material 52 may be represented by thefollowing equation:

${C_{Po} = \frac{ɛ_{Po}ɛ_{0}A}{d_{M}}},$

where ε_(Po) is the relative permittivity of material 52 at frequencyf_(Po) and d_(M) is the thickness of material 52. In some examples, thecontroller may use C_(A) determined in the first measurement, freepermittivity ε₀, and equivalent capacitance C_(eq,Po) to determine thecapacitance C_(Po) of material 52 at frequency f_(Po) to determineε_(Po).

The technique of FIG. 4 may further include determining, by thecontroller, a porosity of material 52 (64). The controller may use anytechnique that determines a property fraction of pore medium fromcapacitance of material 52. In some examples, the controller maydetermine a volume fraction of material 52 and pore medium by evaluatingthe relative permittivity ε_(Po) with respect to a dielectric constantof the pore medium and a dielectric constant of material 52.

The technique of FIG. 4 may include causing, by the controller, anelectrolyte source to deposit electrolyte solution to at least onesurface of material 52. In some examples, the controller may cause theelectrolyte source to immerse material 52 in the electrolyte solution.In other examples, the controller may cause the electrolyte source todeposit electrolyte solution to a top surface of material 52.Electrolyte solution may substantially fill open pores of a portion ofmaterial 52, such as greater than 90% of open pores. Electrolytesolution 52 may also replace air gaps, such as air gap 50, betweencapacitive electrodes 44, 48.

The technique of FIG. 4 may include causing, by the controller,capacitance probe 42 to subject material 52, immersed in electrolytesolution, to an electric signal having the frequency f_(Po) (64). FIG.5C is a diagram of system 80 for measuring a capacitance of material 52immersed in electrolyte solution at frequency f_(Po) for determining aporosity. Capacitance probe 42 may have material 52 and electrolytelayer 82 between capacitance electrodes 44, 48. Electrolyte layer 82 mayhave a thickness D_(E) that replaces air gap 50. Material 52 may have anew thickness d_(M′) due to immersion of electrolyte into material 52.

The technique of FIG. 4 may further include determining, by thecontroller, a capacitance of material 52, immersed in electrolytesolution, at frequency f_(Po) (66). The controller may measure anequivalent capacitance C_(eq,CP) between capacitance electrodes 44, 48,including a closed pore capacitance C_(CP) of material 52 at frequencyf_(Po) and a capacitance C_(E) of electrolyte layer 82. The equivalentcapacitance C_(eq,CP) may be represented by the following equation:

$C_{{eq},{CP}} = \left( {\frac{1}{C_{E}} + \frac{1}{C_{CP}}} \right)^{- 1}$

The capacitance C_(E) of electrolyte layer 82 may be negligible, as apermittivity value of the electrolyte layer may be very low. The closedpore capacitance C_(CP) of material 52 may be represented by thefollowing equation:

${C_{CP} = \frac{ɛ_{CP}ɛ_{0}A}{d_{M\;\prime}}},$

where ε_(CP) is the closed pore permittivity of material 52 at frequencyf_(Po). Due to the negligible permittivity of the electrolyte layer 82,the equivalent capacitance C_(eq,CP) may be equal to the closed porecapacitance C_(CP) of material 52.

The technique of FIG. 4 may further include determining, by thecontroller, a closed porosity and an open porosity of material 52 (68).In some examples, the controller may determine a closed porosity and anopen pore porosity based on the closed pore permittivity cu of material52 at frequency f_(Po) determined above by using multiplemeasurements—in air and in electrolyte. For example, if the relativepermittivity EN of SiC material 52 in air at frequency f_(Po) is 19.5,the relative permittivity ε_(CP) of closed pore SiC material 52 atfrequency f_(Po) is 19, the dielectric constant of air is 1, and thepermittivity of nonporous SiC is 20, then the closed porosity ofmaterial 52 may be about 3.5% and the open porosity of material 52 maybe about 3.5%.

The technique of FIG. 4 may further include causing, by the controller,capacitance probe 42 to be positioned over a different portion ofmaterial 52. Controller 16 may reposition capacitance probe 4 at adifferent portion of material 52 (72). Before step 60 discussed above,the controller may cause capacitance probe 42 to be positioned over aportion of material 52. After determining an open porosity and a closedporosity of material 52, as in step 70, the controller may determineadditional portions of material 52 for which to determine an open orclosed porosity. The controller may cause capacitance probe 42 to bepositioned over a different portion of material 52. The controller maygenerate a representation of an open and closed porosity as a functionof portion of material 52 (74). The controller may cause a userinterface device to output the representation of the open and closedporosity.

By using the technique of FIG. 4, system 2 may quickly and inexpensivelydetermine an open and closed porosity of a material. For example, ratherthan use expensive x-ray tomography, the technique of FIG. 4 may use arelatively inexpensive capacitance probe to determine the open andclosed porosity of a material at various locations. As another example,rather than use more immersive gravimetric methods involving submersionand weighing, the technique of FIG. 4 may allow for targeted applicationof electrolyte solution and analysis for specific portions of amaterial.

In some examples, system 2 of FIG. 1 may be used to determine a phase orlayer composition of material 8 having a coating or other layer. Forexample, material 8 may include a substrate and an environmental barriercoating on the substrate to protect substrate from chemical attack byenvironmental species, such as water vapor or oxygen. System 2 may beused to evaluate the coating for uniformity, to determine whether asufficiently thick coating has been applied to the substrate, or todetermine whether the coating includes an acceptable level of porosity,open porosity, or closed porosity. FIG. 6 is a flow diagram illustratingan example technique for determining phase or layer composition of asecond material, such as a coating, on a first material usingcapacitance (91). The techniques of FIG. 6 will be described withconcurrent reference to FIGS. 7A-7C, although one of ordinary skill willunderstand that the techniques of FIG. 6 may be performed by othersystems that include more or fewer components, and that system 2 mayperform other techniques. FIGS. 7A-7C are diagrams of an example system110 for determining a phase or layer composition of coating 112.Components of FIGS. 7A-7C may be equivalent to similar components ofFIG. 1. For example, system 2, capacitance probe 4, material 8,oscillator 12, capacitance electrodes 18A and 18B, and controller 16 maycorrespond to system 40, capacitance probe 42, material 52, oscillator46, capacitance electrodes 44 and 48, and a controller (not shown),respectively.

FIG. 7A is a diagram of system 110 for measuring a capacitance ofcapacitance probe 42. System 110 may include capacitance probe 42 havingoscillator 46 and capacitance electrodes 44, 48. Before positioning amaterial 52 in air gap 50, a controller (not shown), such as controller16 of FIG. 1, may first determine a free permittivity of capacitanceprobe 42 and air gap 50 by using the capacitance of capacitance probe 42and air gap 50. The controller may cause capacitance probe 42 to subjectair gap 50 to an electric signal. The controller may detect anddetermine a capacitance of the air gap 50. The capacitance may berepresented by the following equation:

${C_{0} = \frac{ɛ_{0}A}{d_{0}}},$

Where C₀ is the capacitance of capacitance probe 42 and air gap 50, ε₀is the free permittivity, A is the area of capacitance electrodes 44,48, and do is a distance between capacitance electrodes 44, 48 filled byair gap 50. The controller may determine the permittivity of free spaceε₀ for capacitance probe 42 and air gap 50.

System 110 may use the techniques of FIG. 6 to determine a phase orlayer composition of second material 112 (91) having at least a firstconstituent phase or layer and a second constituent phase or layer.

The technique of FIG. 6 may include causing, by the controller,capacitance probe 42 to subject material 52 to an electric signal havinga frequency f_(Ph) (90). The frequency f_(Ph) may be selected so thatthe first constituent phase or layer and the second constituent phase orlayer have substantially different dielectric constants at the frequencyf_(Ph). FIG. 7B is a diagram of system 110 for measuring a capacitanceof material 52 at frequency f_(Ph) for determining a phase or layercomposition. Air gap 50 may have a new distance d_(A1) due to spacetaken up by material 52.

The technique of FIG. 6 may further include determining, by thecontroller, a capacitance C_(Ph) of material 52 at frequency f_(Ph),such as in step 28 of FIG. 2 (92). The controller may measure anequivalent capacitance C_(eq,Ph) between capacitance electrodes 44, 48,including a capacitance C_(Ph) of material 52 at frequency f_(Ph) and acapacitance C_(A1) of air gap 50. The equivalent capacitance C_(eq,Ph)may be represented by the following equation:

$C_{{eq},{Ph}} = \left( {\frac{1}{C_{A}} + \frac{1}{C_{Ph}}} \right)^{- 1}$

The capacitance C_(A1) of air gap 50 may be represented by the followingequation:

${C_{A1} = \frac{ɛ_{0}A}{d_{0} - d_{M}}},$

while the capacitance C_(Ph) of material 52 at frequency f_(Ph) may berepresented by the following equation:

${C_{Ph} = \frac{ɛ_{Ph}ɛ_{0}A}{d_{M}}},$

where ε_(Ph) is the relative permittivity of material 52 at frequencyf_(Ph). In some examples, the controller may use the C_(A) determined inthe first measurement, the free permittivity ε₀, and the equivalentcapacitance C_(eq,Ph), at frequency f_(Ph) to determine the capacitanceC_(Ph) and/or relative permittivity ε_(Ph) of material 52 at frequencyf_(Ph).

In some examples, the technique of FIG. 6 may further includedetermining, by the controller, a relative phase composition of material52 (not shown). In some examples, the controller may determine acontribution of each of the first constituent phase dielectric constantand the second constituent phase dielectric constant to the relativepermittivity ε_(Ph) of material 52 at frequency f_(Ph).

The technique of FIG. 6 may further include depositing a secondmaterial, such as coating 112, on material 52 (not shown). For example,an environmental barrier coating may be applied to material 52 toprotect material 52 from deterioration. In some examples, coating 112may have more than one layer deposited. For examples of coating 112, seematerial 8 of FIG. 1.

The technique of FIG. 6 may include causing, by the controller,capacitance probe 42 to subject material 52 and coating 112 to anelectric signal having a frequency f_(Ph) (96). In some examples, thefrequency f_(Ph) may be selected so that the first constituent phase orlayer and the second constituent phase or layer have substantiallydifferent dielectric constants at the frequency f_(Ph). FIG. 7C is adiagram of system 110 for measuring a capacitance of a first materialand a second material at a frequency f_(Ph) for determining a phasecomposition of coating 112. Air gap 50 may have a new distance d_(A2)due to space taken up by material 52 and coating 112.

The technique of FIG. 6 may further include determining, by thecontroller, a capacitance of material 52 at frequency f_(Ph) (98). Thecontroller may measure an equivalent capacitance C_(eq,CoPh) betweencapacitance electrodes 44, 48, including a capacitance C_(Ph) ofmaterial 52 at frequency f_(Ph), a capacitance C_(CoPh) of coating 112at frequency f_(Ph), and a capacitance C_(A2) of air gap 50. Theequivalent capacitance C_(eq,CoPh) may be represented by the followingequation:

${C_{{eq},{CoPh}} = \left( {\frac{1}{C_{A2}} + \frac{1}{C_{Ph}} + \frac{1}{C_{CoPh}}} \right)^{- 1}},$

where the capacitance C_(A2) of air gap 50 may be represented by thefollowing equation:

${C_{A2} = \frac{ɛ_{0}A}{d_{0} - d_{C} - d_{M}}},$

where d_(C) is a thickness of the coating 112. The capacitance C_(CoPh)of coating 112 at frequency f_(Ph) may be represented by the followingequation:

${C_{CoPh} = \frac{ɛ_{CoPh}ɛ_{0}A}{d_{C}}},$

where ε_(CoPh) is the relative permittivity of coating 112 at frequencyf_(Ph). In some examples, the controller may use the free permittivityε₀, the equivalent capacitance C_(eq,CoPh), and the capacitance C_(Ph)of material 52 at frequency f_(Ph), to determine the capacitanceC_(CoPh) of coating 112 at frequency f_(Ph).

The technique of FIG. 6 may further include determining, by thecontroller, a relative composition of coating 112, such as a relativeconstituent or layer composition (100). In other examples having a firstand a second constituent phase, the controller may determine a volumefraction of each of a first constituent phase dielectric constant and asecond constituent phase dielectric constant to the relativepermittivity ε_(CoPh) of coating 112 at frequency f_(Ph). For example,the volume fraction of the first and second constituents of coating 112may be represented by the following equations:ε_(R)=ε_(M,1) V _(M,1)+ε_(M,2) V _(M,2) and V _(M,1) +V _(M,2)=1,

where ε_(M,1) is the relative permittivity of the first constituent,V_(M,1) is the volume fraction of the first constituent, ε_(M,2) is therelative permittivity of the second constituent, and V_(M,2) is thevolume fraction of the second constituent. In others examples having twolayers in coating 112, the controller may determine a relativecomposition of each of a first layer dielectric constant and a secondlayer dielectric constant to the relative permittivity ε_(CoPh) ofcoating 112 at frequency f_(Ph) to determine, for example, a relativethickness of each layer or a uniformity of coverage of each layer acrossmaterial 52.

In some examples, the controller may determine a thickness d_(C) ofcoating 112 based on a known relative permittivity C_(CoPh) of coating112. For example, the controller may determine whether the thicknessd_(C) of coating 112 is uniform over an article. If a capacitanceC_(CoPh) of coating 112 is outside a threshold, indicating a coatingthat is too thick or thin, coating 112 may be rejected.

The technique of FIG. 6 may further include causing, by the controller,capacitance probe 42 to be positioned over a different portion ofmaterial 52. Controller 16 may reposition capacitance probe 4 at adifferent portion of material 52 (102). Before step 90 discussed above,the controller may cause capacitance probe 42 to be positioned over aportion of material 52. After determining relative composition ofcoating 112, as in step 100, the controller may determine additionalportions of coating 112 for which to determine a relative composition.The controller may cause capacitance probe 42 to be positioned over adifferent portion of coating 112. The controller may generate arepresentation of a relative composition as a function of portion ofcoating 112 (104). The controller may cause a user interface device tooutput the representation of the relative composition.

In addition to or instead of determining a phase or layer composition ofa second material on a first material, system 2 of FIG. 1 may alsodetermine a porosity, open porosity, and closed porosity of the secondmaterial. For example, a coating used as an environmental barriercoating may have certain requirements for porosity to restrictpermeation of gases through the environmental barrier coating to theunderlying substrate. FIG. 8 is a flow diagram illustrating an exampletechnique for determining open or closed porosity of a second materialon a first material using capacitance. (121). The technique of FIG. 8will be described with concurrent reference to FIGS. 9A-9D, although oneof ordinary skill will understand that the technique of FIG. 8 may beperformed by other systems that include more or fewer components, andthat system 2 may perform other techniques. FIGS. 9A-9D are diagrams ofan example system 140 for determining a porosity, an open porosity,and/or a closed porosity of a coating 112 on material 52. Components ofFIGS. 9A-9D may be equivalent to similar components of FIG. 1. Forexample, system 2, capacitance probe 4, material 8, oscillator 12,capacitance electrodes 18A and 18B, and controller 16 may correspond tosystem 40, capacitance probe 42, material 52, oscillator 46, capacitanceelectrodes 44 and 48, and a controller (not shown), respectively.

FIG. 9A is a diagram of system 140 for measuring a capacitance ofcapacitance probe 42. Capacitance probe 42 includes oscillator 46 andcapacitance electrodes 44, 48. Before positioning a material 52 in airgap 50, a controller (not shown), such as controller 16 of FIG. 1, mayfirst determine a free permittivity of capacitance probe 42 and air gap50 by using the capacitance of capacitance probe 42 and air gap 50. Thefree permittivity ε₀ represents the electric field permittivity causedby capacitance probe 42 and air gap 50 (e.g., air may have a dielectricconstant of 1). The controller may cause capacitance probe 42 to subjectair gap 50 to an electric signal. The controller may detect anddetermine a capacitance of the air gap 50. The capacitance may berepresented by the following equation:

${C_{0} = \frac{ɛ_{0}A}{d_{0}}},$

Where C₀ is the capacitance of capacitance probe 42 and air gap 50, ε₀is the free permittivity, A is the area of capacitance electrodes 44,48, and do is a distance between capacitance electrodes 44, 48 filled byair gap 50. The controller may determine the free permittivity ε₀ forcapacitance probe 42 and air gap 50.

System 140 may use the techniques of FIG. 8 to determine a porosity of aportion of coating 112 (121). The technique of FIG. 8 may includecausing, by the controller, capacitance probe 42 to subject material 52to an electric signal having a frequency f_(Po) (120). The frequencyf_(Ph) may be selected so that the first constituent phase or layer andthe second constituent phase or layer have substantially differentdielectric constants at the frequency f_(Ph).

FIG. 9B is a diagram system 140 for measuring a capacitance of material52 at frequency f_(Po) for determining a porosity. The portion of thematerial 52 may be the portion between capacitance electrodes 44, 48.Material 52 may have a thickness d_(M), while air gap 50 may have a newthickness d_(A1) due to space taken up by material 52. Material 52 mayhave a single constituent phase, or material 52 may have two or moreconstituent phases.

The technique of FIG. 8 may further include determining, by thecontroller, a capacitance of material 52 at the frequency f_(Po) (122).The controller may measure an equivalent capacitance C_(eq,Po) betweencapacitance electrodes 44, 48, including a capacitance C_(Po) ofmaterial 52 at frequency f_(Po) and a capacitance C_(A1) of air gap 50.The equivalent capacitance C_(eq,Ph) may be represented by the followingequation:

$C_{{eq},{Po}} = {\left( {\frac{1}{C_{A}} + \frac{1}{C_{Po}}} \right)^{- 1}.}$

The capacitance C_(A1) of air gap 50 may be represented by the followingequation:

${C_{A1} = \frac{ɛ_{0}A}{d_{0} - d_{M}}},$

while the capacitance C_(Po) of material 52 at frequency f_(Po) may berepresented by the following equation:

${C_{Po} = \frac{ɛ_{Po}ɛ_{0}A}{d_{M}}},$

where ε_(Po) is the relative permittivity of material 52 at frequencyf_(Po). In some examples, the controller may use the capacitance C_(A)of the first measurement, the free permittivity ε₀, and the equivalentcapacitance C_(eq,Po), to determine the capacitance C_(Po) and/orrelative permittivity ε_(Po) of material 52 at frequency f_(Po).

The technique of FIG. 8 may further include depositing a secondmaterial, such as coating 112, on material 52 (not shown). For example,an environmental barrier coating may be applied to material 52 toprotect material 52 from deterioration. In some examples, coating 112may have more than one layer deposited. For examples of coating 112, seematerial 8 of FIG. 1. Air gap 50 may have a new distance d_(A2) due tospace taken up by material 52 and coating 112.

The technique of FIG. 6 may include causing, by the controller,capacitance probe 42 to subject material 52 and coating 112 to anelectric signal having a frequency f_(Po) (124). In some examples, thefrequency f_(Po) may be selected so that the first constituent phase orlayer and the second constituent phase or layer have substantiallysimilar dielectric constants at the frequency f_(Po). FIG. 9C is adiagram system 140 for measuring a capacitance of material 52 andcoating 112 at a frequency f_(Po) for determining a porosity.

The technique of FIG. 8 may further include determining, by thecontroller, a capacitance of material 52 and coating 112 at thefrequency f_(Po) (126). The controller may measure an equivalentcapacitance C_(eq,CoPo) between capacitance electrodes 44, 48, includinga capacitance C_(Po) of material 52 at frequency f_(Po), a capacitanceC_(CoPo) of coating 112 at frequency f_(Po), and a capacitance C_(A2) ofair gap 50. The equivalent capacitance C_(eq,CoPo) may be represented bythe following equation:

$C_{{eq},{CoPo}} = {\left( {\frac{1}{C_{A2}} + \frac{1}{C_{Po}} + \frac{1}{C_{CoPo}}} \right)^{- 1}.}$

The capacitance C_(A2) of air gap 50 may be represented by the followingequation:

${C_{A2} = \frac{ɛ_{0}A}{d_{0} - d_{C} - d_{M}}},$

where d_(C) is a thickness of the coating 112. The capacitance C_(CoPo)of material 52 at frequency f_(Po) may be represented by the followingequation:

${C_{CoPo} = \frac{ɛ_{CoPo}ɛ_{0}A}{d_{C}}},$

where C_(CoPh) is the relative permittivity of coating 112 at frequencyf_(Po). In some examples, the controller may use the permittivity offree space co, the equivalent capacitance C_(eq,CoPo), and thecapacitance C_(Po) of material 52 at frequency f_(Po), to determine thecapacitance C_(CoPo) of coating 112 at frequency f_(Po).

The technique of FIG. 8 may further include determining, by thecontroller, a porosity of coating 112 (128). The controller may use anytechnique that determines a property fraction of pore medium fromcapacitance of material 52. In some examples, the controller maydetermine a volume fraction of material 52 and pore medium by evaluatingthe relative permittivity ε_(Po) with respect to a dielectric constantof the pore medium and a dielectric constant of material 52.

The technique of FIG. 8 may include causing, by the controller, anelectrolyte source to deposit electrolyte solution to at least onesurface of coating 112 (not shown). In some examples, the controller maycause the electrolyte source to immerse coating 112 in the electrolytesolution. In other examples, the controller may cause the electrolytesource to deposit electrolyte solution to a top surface of coating 112.Electrolyte solution may substantially fill open pores of a portion ofcoating 112, such as greater than 90% of open pores. Electrolytesolution 52 may also replace air gaps, such as air gap 50, betweencapacitive electrodes 44, 48.

FIG. 9D is a diagram of system 140 for measuring a capacitance ofmaterial 52 and coating 112 immersed in electrolyte solution at afrequency f_(Po) for determining a porosity. Material 52, coating 112,and electrolyte layer 82 may be positioned between capacitanceelectrodes 44, 48. Electrolyte layer 82 may have a thickness D_(E) thatreplaces air gap 50. Coating 112 may have a new thickness d_(C′) due toimmersion of electrolyte into coating 112. The technique of FIG. 8 mayinclude causing, by the controller, capacitance probe 42 to subjectmaterial 52, immersed in electrolyte solution, to an electric signalhaving the frequency f_(Po) (130).

The technique of FIG. 8 may further include determining, by thecontroller, a capacitance of material 52 and coating 112, immersed inelectrolyte solution, at the frequency f_(Po) (132). The controller maymeasure an equivalent capacitance C_(eq,CoCP) between capacitanceelectrodes 44, 48, including a capacitance C_(Po) of material 52, aclosed pore capacitance C_(CoCP) of coating 112, and a capacitance C_(E)of electrolyte layer 82. The equivalent capacitance C_(eq,CoCP) may berepresented by the following equation:

$C_{{eq},{CoCP}} = \left( {\frac{1}{C_{E}} + \frac{1}{C_{Po}} + \frac{1}{C_{CoCP}}} \right)^{- 1}$

The capacitance C_(E) of electrolyte layer 82 may be negligible, as apermittivity value of the electrolyte layer may be very low.

The closed pore capacitance C_(CoCP) of coating 112 may be representedby the following equation:

${C_{CoCP} = \frac{ɛ_{CoCP}ɛ_{0}A}{d_{C\;\prime}}},$

where ε_(CoCP) is the closed pore permittivity of coating 112 atfrequency f_(Po). Due to the negligible permittivity of the electrolytelayer 82, the equivalent capacitance C_(eq,CoCP) may be related to thecapacitance C_(Po) of material 52 at frequency f_(Po) and the closedpore capacitance C_(CoCP) of coating 112 at frequency f_(Po).

The technique of FIG. 8 may further include determining, by thecontroller, a closed porosity and an open porosity of material 52 (134).In some examples, the controller may determine a volume fraction ofclosed pores and open pores by evaluating the closed pore relativepermittivity ε_(Po) of material coating 112 at frequency f_(Po) withrespect to the porosity of coating 112.

The technique of FIG. 8 may further include causing, by the controller,capacitance probe 42 to be positioned over a different portion ofmaterial 52. Controller 16 may reposition capacitance probe 4 at adifferent portion of material 52 (136). Before step 120 discussed above,the controller may cause capacitance probe 42 to be positioned over aportion of material 52. After determining a capacitance of the firstmaterial, as in step 122, or an open porosity and a closed porosity ofmaterial 52, as in step 134, the controller may determine additionalportions of material 52 for which to determine an open or closedporosity. The controller may cause capacitance probe 42 to be positionedover a different portion of material 52. The controller may generate arepresentation of relative composition as a function of portion ofcoating 112 (138). The controller may cause a user interface device tooutput the representation of the relative composition.

The techniques discussed in FIGS. 2-9 may be further used to determinematerial properties for more than one portion of a material. Forexample, gantry system 14 of FIG. 1 may move capacitance probes 4 and 42to different portions of a material 8 and 52 to determine a spatial mapof material 8 and 52. The spatial map may include spatial compositionalinformation of the material, such as capacitance, permittivity,porosity, phase composition, layer composition, open/closed porosity,and the like. The spatial information may be stored, for example, in adata base and any changes in the materials may be tracked. For example,a thickness of coating 112 of FIG. 7 may be tracked over time to monitorcoating 112 for deterioration. In other examples, the spatial map maydetermine variation in the spatial information. For example, a materialor coating may have a specific variance tolerance over an entire area ofthe material or coating. The spatial map may have a spatial resolutionwhich may depend on, for example, physical dimensions of the capacitanceprobe, such as capacitance electrode area and geometry.

FIG. 11 is a diagram of an example system 150 for determining acompositional property of a material, such as material 158 and coating156, using capacitance. Components of FIG. 11 may be substantially thesame as similar components of FIG. 1. For example, system 2, vessel 6,material 8, gantry system 14, and capacitance electrodes 18A and 18B maycorrespond to system 150, a vessel 168, material 158 and coating 156, agantry system 166, and capacitance electrode(s) 164, respectively.System 150 may include vessel 168 to house material 158 and coating 156.Vessel 168 includes gantry system 166 for moving two or more capacitanceelectrodes 164 of a capacitance probe to different portions of material158 and coating 156. An insulated clamping mechanism 162 may securematerial 158 and coating 156, while an insulated stand 160 may secureinsulated clamping mechanism 162 to vessel 168. An O-ring/guard ringstructure 154 may create a seal around capacitance electrode 164contacting electrolyte solution 152.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method, comprising: causing, by a controller, acapacitance probe to subject a material to an electric signal having afrequency, wherein the material includes a first solid constituent phaseand a second solid constituent phase, and wherein the first solidconstituent phase and the second solid constituent phase havesubstantially different dielectric constants at the frequency;determining, by the controller, a capacitance of the material; anddetermining, by the controller, a relative phase composition of thefirst solid constituent phase and the second solid constituent phasebased on the capacitance.
 2. The method of claim 1, wherein determiningthe relative phase composition further comprises determining acontribution of each of a first dielectric constant of the first solidconstituent phase and a second dielectric constant of the second solidconstituent phase to a permittivity of the material at the frequency. 3.The method of claim 1, wherein the first solid constituent phasecomprises a first layer and the second solid constituent phase comprisesa second layer overlying the first layer, and wherein determining therelative phase composition comprises determining a relative thickness ofthe first layer and the second layer.
 4. The method of claim 3, furthercomprising determining, by the controller, a thickness of the secondlayer based on a thickness of the first layer and the relative thicknessof the first layer and the second layer.
 5. The method of claim 1,wherein determining the relative phase composition of the first solidconstituent phase and the second solid constituent phase based on thecapacitance further comprises: determining, by the controller, apermittivity of the first solid constituent phase and the second solidconstituent phase; and determining, by the controller, the relativephase composition of the material based on the permittivity of the firstsolid constituent phase and the second solid constituent phase based onequation:ε_(R)=ε_(M,1) V _(M,1)+ε_(M,2) V _(M,2) where ε_(M,1) is a relativepermittivity of the first solid constituent phase, V_(M,1) is a volumefraction of the first solid constituent phase, ε_(M,2) is a relativepermittivity of the second solid constituent phase, and V_(M,2) is avolume fraction of the second solid constituent phase.
 6. The method ofclaim 1, wherein the electric signal comprises a first electric signal,and wherein the capacitance comprises a first capacitance, the methodfurther comprising: causing, by the controller, the capacitance probe tobe positioned over a different portion of the material; causing, by thecontroller, the capacitance probe to subject the different portion ofthe material to a second electric signal having the frequency;determining, by the controller, a second capacitance of the differentportion of the material; and determining, by the controller, a relativephase composition of the first solid constituent phase and the secondsolid constituent phase of the second portion of the material based onthe second capacitance.
 7. The method of claim 1, further comprising:generating, by the controller, a representation of relative phasecomposition of the first solid constituent phase and the second solidconstituent phase as a function of portion of the material; and causing,by the controller, a user interface device to output the representationof relative phase composition.
 8. The method of claim 1, wherein theelectric signal is a first electric signal, wherein the frequency is afirst frequency, and wherein the method further comprises: causing, bythe controller, the capacitance probe to subject the material to asecond electric signal having a second frequency, wherein the firstsolid constituent phase and the second solid constituent phase havesubstantially similar dielectric constants at the second frequency;determining, by the controller, a second capacitance of the material atthe second frequency; and determining, by the controller, a porosity ofthe material based on the second capacitance.
 9. A method, comprising:causing, by a controller, a capacitance probe to subject a firstmaterial to a first electric signal; determining, by the controller, afirst capacitance of the first material; causing, by a controller, acapacitance probe to subject the first material and a second material toa second electric signal having a frequency, wherein the second materialincludes a first constituent phase and a second constituent phase, andwherein the first constituent phase and the second constituent phasehave substantially different dielectric constants at the frequency;determining, by the controller, a second capacitance of the firstmaterial and the second material; determining, by the controller, arelative phase composition of the first constituent phase and the secondconstituent phase of the second material based on the first capacitanceand the second capacitance.
 10. The method of claim 9, whereindetermining the relative phase composition further comprises determininga contribution of each of a first dielectric constant of the firstconstituent phase and a second dielectric constant of the secondconstituent phase to a permittivity of the second material at thefrequency.
 11. The method of claim 9, wherein the first constituentphase comprises a first layer and the second constituent phase comprisesa second layer overlying the first layer, and wherein determining therelative phase composition comprises determining a relative thickness ofeach layer of the second material or a relatively uniformity of eachlayer of the second material.
 12. The method of claim 9, whereindetermining, by the controller, the relative phase composition of thefirst constituent phase and the second constituent phase of the secondmaterial based on the capacitance further comprises: determining, by thecontroller, a permittivity of the first constituent phase and the secondconstituent phase; and determining, by the controller, the relativephase composition of the second material based on the permittivity ofthe first constituent phase and the second constituent phase based onequation:ε_(R)=ε_(M,1) V _(M,1)+ε_(M,2) V _(M,2) where ε_(M,1) is a relativepermittivity of the first constituent phase, V_(M,1) is a volumefraction of the first constituent phase, ε_(M,2) is a relativepermittivity of the second constituent phase, and V_(M,2) is a volumefraction of the second constituent phase.
 13. The method of claim 9,further comprising: causing, by the controller, the capacitance probe tobe positioned over a different portion of the second material; causing,by the controller, the capacitance probe to subject the differentportion of the second material to a third electric signal having thefrequency; determining, by the controller, a third capacitance of thedifferent portion of the second material; and determining, by thecontroller, a relative phase composition of the first constituent phaseand the second constituent phase of the second portion of the secondmaterial based on the third capacitance.
 14. The method of claim 9,further comprising: generating, by the controller, a representation ofrelative phase composition of the first constituent phase and the secondconstituent phase as a function of portion of the second material; andcausing, by the controller, a user interface device to output therepresentation of relative phase composition.
 15. The method of claim 9,further comprising depositing the second material on the first material.16. The method of claim 9, wherein the frequency is a first frequency,and wherein the method further comprises: causing, by the controller,the capacitance probe to subject the first and the second material to athird electric signal having a second frequency, wherein the firstconstituent phase and the second constituent phase of the secondmaterial have substantially similar dielectric constants at the secondfrequency; determining, by the controller, a third capacitance of thematerial at the second frequency; and determining, by the controller, aporosity of the material based on the third capacitance.
 17. A system,comprising: a capacitance probe; and a controller communicativelycoupled to the capacitance probe, wherein the controller is configuredto: cause the capacitance probe to subject a material to an electricsignal having a frequency, wherein the material includes a first solidconstituent phase and a second solid constituent phase, and wherein thefirst solid constituent phase and the second solid constituent phasehave substantially different dielectric constants at the frequency;determine a capacitance of the material; and determine a relative phasecomposition of the first solid constituent phase and the second solidconstituent phase based on the capacitance.
 18. The system of claim 17,wherein the controller is further configured to control a gantry systemto position the capacitance probe over a different portion of thematerial.
 19. The system of claim 18, wherein the controller is furtherconfigured to: generate a representation of relative phase compositionof the material as a function of position of the material; and cause auser interface device to output the representation of relative phasecomposition.
 20. The system of claim 17, wherein the electric signal isa first electric signal, wherein the frequency is a first frequency, andwherein the controller is further configured to: cause the capacitanceprobe to subject the material to a second electric signal having asecond frequency, wherein the first solid constituent phase and thesecond solid constituent phase have substantially similar dielectricconstants at the second frequency; determine a second capacitance of thematerial at the second frequency; and determine a porosity of thematerial based on the second capacitance.